Pilferage control system

ABSTRACT

An antipilferage system comprising a cooperating radio frequency transmitter and receiver pair. The transmitter directs swept radio frequency energy to the cooperating receiver circuit wherein balanced oscillating conditions are maintained in a normally steady state. Passive tuned circuits, preferably in the form of printed circuit elements are placed on the merchandise in a store and if an attempt is made to remove unpurchased merchandise from the store without first destroying a fusible link in the passive tuned circuit an unbalance is caused in the receiver oscillator circuits which operates to actuate a suitable alarm. A fully automatic deactivation circuit is also included as part of the invention.

United States Patent 12 Claims, 3 Drawing Figs.

U.S. Cl 340/280, 340/258 R, 340/258 C, 343/6.5 SS

Int. Cl. ..G08b 13/00, G08b 2 H00 Field of Search 340/258 R,

280; 343/65 SS, 6.8 R

[56] References Cited UNITED STATES PATENTS 3,493,955 2/1970 Minasy340/258 R 3,363,247 1/1968 Chausse et al. 343/65 SS PrimaryExaminer-Donald J. Yusko Assistant Examiner-Michael SlobaskyArrorney-Louis Etlinger ABSTRACT: An antipilferage system comprising acooperating radio frequency transmitter and receiver pair. The transmitter directs swept radio frequency energy to the cooperating receivercircuit wherein balanced oscillating conditions are maintained in anormally steady state. Passive tuned circuits, preferably in the form ofprinted circuit elements are placed on the merchandise in a store and ifan attempt is made to remove unpurchased merchandise from the storewithout first destroying a fusible link in the passive tuned circuit anunbalance is caused in the receiver oscillator circuits which operatesto actuate a suitable alarm. A fully automatic deactivation circuit isalso included as part of the invention.

l DUAL J PASSBAND TIME RECEIVER CONSTANT DETECTOR I 22 l I PASSBAND IFILTER I 32 l l CORRELATION I CIRCUIT I FOOT swn'cn PATENTED nuvso l9?!ANTENNA RECEIVE TR ANSMIT ANTENNA DRIVER PASSBAND RECEIVER DUAL TIMECONSTANT DETECTOR PASSBAND 34 FILTER CORRELATION cmcurr I 28 l l l ISWEEP CONTROL FOOT SWITCH mvsurons MARC CHOMET DONALD E. ELLlSON ROBERTF. WATTERSON .ar y I AGENT PATENTEfluuvaolsn sumenr 2 TRANSMIT ANTENNAr58 RECEIVE ANTENNA 3 se SWEEP POWER R L DRIVER RECEIVER RECEIVER 64DEACTIVATION IC V c o BUFFER CONTROL so LOGIC MANUAL DESTRUCT 68 FIG. 5

INVENTORS' MARC CHOMET DONALD E. LusoN ROBERT F. WATTERSON AGENTPILFERAGE CONTROL SYSTEM BACKGROUND OF THE INVENTION The presentinvention relates generally to the field of radiofrequency circuits andmore specifically to a radiofrequency antipilferage system.

DESCRIPTION OF THE PRIOR ART Pilferage of merchandise from businessestablishments has become a matter of great concern and many deviceshave been devised in an attempt to minimize losses. One such device is aDetecting Means for Stolen Goods described in U.S. Pat. No. 2,774,060which issued to T. F. Thompson on Dec. 11, 1956. In this system one ormore fixed frequency oscillators are employed to set up a radiationfield of predetermined shape and size and precision resonant circuitsare concealed in sales tags on the merchandise. When merchandise with aresonant circuit is passed through the radiation field the potential ofthe oscillator is changed and actuation of an alarm results. In order toprevent false alarms by legitimately purchased merchandise it isnecessary that the sales tag containing the circuit be physicallydestroyed.

Several practical problems attend the use of an antipilferage systemsuch as that described by Thompson. The use of a fixed frequencyoscillator requires that the resonant tuned circuit be precision tunedto that frequency. In order to prevent actuation of the alarm by anobject of appropriate size carried by a legitimate customer it isdesirable to use three different fixed frequency oscillators and threeprecision tuned circuits, one for each frequency. In such an arrangementwherein frequency precision is required a serious problem may arise indetuning of the tuned circuit by body capacity, i.e., the electricalcapacity of the human body in close proximity to the tuned circuit is inmany cases sufficient to detune the circuit to the extent that detectionby a single frequency system is precluded. It will be noted that even inthe three oscillator embodiment of the Thompson apparatus detuning ofany of the precision circuits will preclude detection. The fact that theThompson apparatus necessitates a manual destruction of the tunedcircuit bearing tag increases the potential for inadvertent andembarrassing triggering of the alarm should an employee forget to removethe tag. An accomplished pilferer may also become aware of the grossnature of the system from observation of consistent removal of such tagsand/or the consequences of nonremoval. The apparatus described byThompson further involves the use of one antenna for both transmittingthe radiation pattern and detecting an absorption by the resonantcircuit. Such an arrangement has an inherently low-volumetric efiiciencyand the tuned circuit must pass in close proximity to the antenna forreliable detection. Many business establishments are not physically laidout such as to assure such proximity.

OBJECTIVES AND SUMMARY OF THE INVENTION From the foregoing it will beunderstood that among the objectives of the present invention are thefollowing:

To provide a new and novel radiofrequency antipilferage system.

To provide apparatus of the above-described character using a sweptradiofrequency.

To provide apparatus of the above-described character having acooperating transmitter and receiver remotely disposed with respect toone another.

To provide apparatus of the above-described character wherein a passivetuned circuit disposed on merchandise may be automatically andsurreptitiously deactivated.

To provide apparatus of the above-described character having improvedfalse alarm rejection.

The foregoing objectives are accomplished through the practice of thepresent invention by providing a swept radiofrequency oscillator andtransmitting antenna and a remotely disposed cooperating broad bandradiofrequency receiver and antenna coupled to a post detection signalprocessor. A passive tuned circuit having a fusible link is affixed toarticles of merchandise preferably within a price tag or other itemaffixed by the store. When pilfered merchandise bearing the tunedcircuit is carried between the transmitter and receiver there isabsorption of energy from the radiation field and an unbalance isproduced in the receiver which is used to actuate a suitable alarm. Topreclude actuation of the alarm by tags or legitimately purchasedmerchandise each passive tuned circuit is provided with a fusible linkwhich is opened when the circuit is exposed to radiofrequency energyabove a preselected level. To accomplish the deactivation sweptradiofrequency energy above the preselected level is transmitted forexample through the surface of a check out counter at which purchasedmerchandise is wrapped. This energy destroys the fusible link in thepassive tuned circuit and automatically checks for the continuedpresence of an active circuit. Thereafter the merchandise with the tagbearing the deactivated tuned circuit, and in which there has been nochange which is readily discemable to the casual observer, may passbetween the transmitter and receiver without actuating the alarm. Thedeactivation portion of the invention is fully automatic in operationand under normal circumstances completely eliminates any requirement formanual participation of sales employees in the deactivation of the tunedcircuit.

These and other objects, features and advantages of the presentinvention will become more apparent from the detailed discussion takenin conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of apilferage control system in accordance with the present invention.

FIG. 2 is a schematic diagram of a fusible tuned circuit for use withthe present invention.

FIG. 3 is a schematic block diagram of a deactivation circuit for use inthe practice of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT Turning now to FIG. 1 here isillustrated a block diagram of the cooperating transmitter and receiverportions of the present invention which would be placed across each exitof a store. The transmitter generally designated 10 comprises a voltagecontrolled oscillator 12 the output frequency of which is controlled bya sweep control means 14. The swept radiofrequency output signal fromthe oscillator 12 is coupled through a driver 16 to a transmitterantenna 18. A radiation field 20 over a desired area defined by thecharacteristics of the transmitter antenna 18 is thus established. Thetransmitter 10 is preferably placed on one side of the entrance/exit tothe place of business.

The receiver designated generally at 22 is placed on the opposite sideof the store entrance/exit from the transmitter. A receiver antenna 24picks up the swept radiofrequency energy and is coupled to a passbandradio receiver 26. The output of the receiver 26 is applied to a postdetection processor 28 which comprises in sequence a dual time constantdetector 30, amplifier 32, passband filter 34 and correlation circuit36.

The receiver 26 output in the absence of a tuned circuit in theradiation field will be substantially at a continuous level as thetransmitter oscillator 12 is swept in frequency. When a tuned circuitenters the radiation field 20 there will result a discemable dip in thereceiver 26 output due to energy absorption by the circuit at thefrequency for which it is tuned. The dual time constant detector 30operates to reject false absorption signals of two types; first, thatcaused by an individual merely passing through the exit and which ismanifested as an absorption at all frequencies within the sweep range ofthe oscillator 12 and second, the random noise within any electronicsystem which is characterized by very sharp spikes. In that thefrequency is swept rather than fixed the dual time constant detector 30may simply reject any detected absorption which is of too long or shorta duration; i.e. corresponding to either too wide or too narrowfrequency bands to be produced by a tuned circuit in the radiation field20.

Thus receiver signals which have the proper frequency (and thus time)characteristics are coupled to amplifier 32 and thence through apassband filter 34 to a correlation circuit 36. The correlation circuit36 may, for example, comprise a plurality of one shot multivibrators orany other of the recognized means for dividing the frequency sweep ofoscillator 12 into a given number of bins or windows. Once the presenceof a tuned circuit is detected in the radiation field 20 by a properabsorption characteristic the correlation circuit 36 establishes afrequency window or bin; eg percent of the total frequency sweep range,within which the absorption was detected. Only after a predeterminednumber of sequential detections have occurred in that frequency windowwill the correlation circuit 39 produce an output signal. A transientsignal in the system is thus rejected since it would not appear in therequisite number of successive sweeps and random signals would not havethe frequency stability to appear in the same window for a long enoughperiod to actuate the alarm. The correlation circuit output signal couldbe coupled directly to a suitable alarm 40, however, as an added falsealarm rejection feature this signal may be applied to an AND-gate 38 towhich is also coupled a signal from a foot switch (not shown) concealedfor example under a floor mat in an exit doorway. In this fashion thealarm 40 would only be actuated by a person in the radiation field whowas carrying merchandise bearing an active tuned circuit.

FIG. 2 is a schematic illustration of a passive tuned circuit which isuseful in the practice of the present invention. The circuit isessentially a simple tank circuit comprising a coil 42 and capacitors 44and 46. A significant difference, however, which is of great practicalutility in the practice of this invention is the incorporation of afusible link 48 in the circuit. This link is shown for the purpose ofillustration as being disposed between capacitors 44 and 46, however, itis to be understood that disposition anywhere in the circuit is equallysuitable in the practice of the invention. The link 48, when placed inseries in the tuned circuit, has negligible current induced therein bythe radiation field across the entrance/exit of the store and thus hassubstantially no effect upon the detection process discussed above. Thefusible link 48 is formed of a fine conductor such as steel wire whichmay be burned out" by a preselected level of radiofrequency energy. Thepassive tuned circuit may be formed using printed circuit techniqueswell known in the art and incorporated into any of the variety of cards,tags or the like which are normally found in or on merchandise displayedfor sale. Initially the circuit is complete and when placed in aradiation field 20 operates to absorb energy in the field. On theapplication of a relatively higher power RF field the induction fieldoverloads the fusible link, opening the circuit and thus rendering itineffective as an absorber.

FIG. 3 is a schematic block diagram of a fully automatic deactivationcircuit which is preferred in the practice of the present invention.This circuit may be placed beneath the checkout and wrapping counterusually found in business establishments and operates to detect thetuned circuit carried by merchandise being legitimately purchased,switch to an output power sufficient to burnout or open the fusible linkand check to assure that deactivation has actually been accomplished. Avoltage controlled oscillator 50 having substantially the same frequencyrange as oscillator 12 of FIG. 1 and which is controlled by a frequencysweep control means 52 is coupled through a buffer amplifier 54 to apower driver 56. The power driver 56 is coupled to a transmitter antenna58 which may be flush-mounted in or under the wrapping counter. Mountedconcentrically with the transmitter antenna 58 is a receiver antenna 60.When a piece of merchandise bearing a tuned circuit is placed on thewrapping counter an unbalance is produced in the receiver 62 to whichthe receiver antenna 60 is coupled. The receiver output is coupledthrough receiver logic circuitry 64 to a deactivation control logiccircuit 66. When the presence of a tuned circuit is detected thereceiver logic circuit 64 generates an output signal which is applied tothe deactivation control logic circuit 66 which operates to switch thepower driver 56 into a relatively highpower mode (e.g., I00 mw.) for apredetermined period of time. At the end of this time the power drive 56is returned to its normal lower level output. If the continued presenceof a tuned circuit is indicated the deactivation process isautomatically repeated. If, after a predetermined number of deactivationcycles, as determined by feeding back the output of the deactivationcontrol logic circuit 66 to the receiver logic circuit 64, a tunedcircuit continues to be detected a manual destruct indicator 68 such asa light, buzzer or the like, may be activated to instruct the employeeto manually remove and destroy the circuit-bearing tag or label. Tofurther discourage the employee from simply ignoring the manual tagdestruction indicator a reset switch (not shown) may be provided whichmust be closed by the employee before the indicator will be deactivated.The deactivation circuit is thus both fully automatic and self-checkingin operation, and substantially precludes the actuation of theentrance/exit alarm by legitimately purchased merchandise. It is only inrare instances that the manual involvement of an employee is requiredand even in this event the employee need have little if any knowledge ofwhat the under-counter unit is or how it operates.

It will thus be seen that the objectives set forth hereinabove, amongthose made apparent from the preceding description are efficientlyattained and since certain changes may be made in the above constructionwithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in the appendeddrawings shall be interpreted as illustrative and not in a limitingsense.

Having described what is new and novel and desired to secure by LettersPatent, what is claimed is:

I. A pilferage control system for detecting the unauthorized removal ofgoods from an area comprising a passive tank circuit affixed to saidgoods, tuned such as to have predetermined radiofrequency absorptioncharacteristics in the presence of a radiation field, and having fusiblelink disposed in series therein,

means for transmitting a field of swept radiofrequency radiation of apreselected first level into a volume of space including an exit fromsaid area, means disposed remotely with respect to said transmittingmeans for detecting said swept radiofrequency radiation and responsiveto a selected change in said radiation level to produce an electricaloutput signal indicative thereof,

tuned circuit deactivation means for selectively applying sweptradiofrequency frequency radiation of a preselected second level higherthan said first level to said passive tank circuit said second levelbeing sufficiently high to destroy said fusible link, and

indicating means coupled to said detecting means and responsive to saidelectrical output signal therefrom to indicate the presence ofa passivetuned tank circuit having a complete fusible link therein within saidradiation field.

2. Apparatus as recited in claim I wherein said transmitting meanscomprises a variable radiofrequency oscillator,

means coupled to said oscillator for varying the frequency thereof as apreselected function of time,

a planar radiofreqnecy transmitting antenna, and

means for driving said antenna coupled between said oscillator and saidantenna.

3. Apparatus as recited in claim 1 wherein said detecting meanscomprises a planar radiofrequency receiving antenna,

a radiofrequency passband receiver coupled to said receiving antenna,and

means coupled to said receiver for rejecting detected changes in saidradiation level which correspond to other than absorption produced by apassive tank circuit in said radiation field.

4. Apparatus as recited in claim 3 wherein said rejecting means includesa dual time constant detector means operative to produce an electricaloutput signal only in response to detected changes in said radiationlevel which correspond to the presence of a passive tuned tank circuithaving a complete fusible link in said radiation field, and to rejectdetected changes both above and below a preselected frequency bandwidth.

5. Apparatus as recited in claim 4 wherein said rejecting means includescorrelation means coupled to said dual time constant detector meanscomprising means for establishing a plurality of frequency bands withinthe frequency range of said transmitting means,

means for determining in which one of said plurality of frequency bandsa change in said radiation level corresponding to the presence of apassive tuned tank circuit is produced,

means for detecting only changes in said radiation level which occur insaid one frequency band for a predetermined number of sequential sweepsthrough said frequency range of said transmitting means, and

means for producing an electrical output signal only in response to saidpredetermined number of sequential detections in said one frequencyband.

6. Apparatus as recited in claim 1 further including means coupledbetween said detecting means and said indicating means for sensing thepresence of a person in said radiation field and producing an electricalsignal indicative thereof and wherein said indicating means isresponsive only to the combined electrical signals from said detectingmeans and said sensing means.

7. Apparatus as recited in claim 1 wherein said passive tuned tankcircuit comprises in series an inductance element,

first and second capacitive elements, and

a fusible link disposed in said circuit and susceptible to destructionby the application of radiofrcquency energy above a preselected level.

8. Apparatus as recited in claim 1 wherein said tuned circuitdeactivation means comprises means for transmitting swept radiofrequency radiation at selectable first and second levels into apreselected volume of space,

means colocated with said transmitting means for detecting said sweptradiofrcquency radiation and responsive to a selected change in saidradiation level to produce an electrical output signal indicative of thepresence of said tuned circuit, and

means coupled to said detecting means and to transmitting means forselecting the higher of said first and second transmitting means outputradiation levels for a preselected period of time said higher levelbeing sufficiently high to burnout said fusible link in said tunedcircuit.

9. Apparatus as recited in claim 8 further including means forindicating complete destruction of said fusible link.

10. A tuned passive tank circuit for use with a radiofrcquency pilferagecontrol system comprising in series an inductance element,

first and second capacitive elements, and

a fusible link disposed in said circuit and susceptible to destructionby the application of radiofrequency radiation above a preselectedlevel.

11. Apparatus as recited in claim 10 wherein said fusible link is formedof an electrically conductive material wherein an electrical overloadadequate to destroy said link is induced by a radiofrcquency radiationlevel of one hundred milliwatts.

12. Apparatus as recited in claim 10 wherein:

said radio frequency pilferage control system employs swept radiofrequency radiation, and

said tuned passive tank circuit is tuned such as to absorb radiationover a frequency range less than and within the range ofradiofrequencies frequencies over which said pilferage control system isswept.

l t l I?

1. A pilferage control system for detecting the unauthorized removal ofgoods from an area comprising a passive tank circuit affixed to saidgoods, tuned such as to have predetermined radiofrequency absorptioncharacteristics in the presence of a radiation fiEld, and having fusiblelink disposed in series therein, means for transmitting a field of sweptradiofrequency radiation of a preselected first level into a volume ofspace including an exit from said area, means disposed remotely withrespect to said transmitting means for detecting said sweptradiofrequency radiation and responsive to a selected change in saidradiation level to produce an electrical output signal indicativethereof, tuned circuit deactivation means for selectively applying sweptradiofrequency radiation of a preselected second level higher than saidfirst level to said passive tank circuit said second level beingsufficiently high to destroy said fusible link, and indicating meanscoupled to said detecting means and responsive to said electrical outputsignal therefrom to indicate the presence of a passive tuned tankcircuit having a complete fusible link therein within said radiationfield.
 2. Apparatus as recited in claim 1 wherein said transmittingmeans comprises a variable radiofrequency oscillator, means coupled tosaid oscillator for varying the frequency thereof as a preselectedfunction of time, a planar radiofrequency transmitting antenna, andmeans for driving said antenna coupled between said oscillator and saidantenna.
 3. Apparatus as recited in claim 1 wherein said detecting meanscomprises a planar radiofrequency receiving antenna, a radiofrequencypassband receiver coupled to said receiving antenna, and means coupledto said receiver for rejecting detected changes in said radiation levelwhich correspond to other than absorption produced by a passive tankcircuit in said radiation field.
 4. Apparatus as recited in claim 3wherein said rejecting means includes a dual time constant detectormeans operative to produce an electrical output signal only in responseto detected changes in said radiation level which correspond to thepresence of a passive tuned tank circuit having a complete fusible linkin said radiation field, and to reject detected changes both above andbelow a preselected frequency bandwidth.
 5. Apparatus as recited inclaim 4 wherein said rejecting means includes correlation means coupledto said dual time constant detector means comprising means forestablishing a plurality of frequency bands within the frequency rangeof said transmitting means, means for determining in which one of saidplurality of frequency bands a change in said radiation levelcorresponding to the presence of a passive tuned tank circuit isproduced, means for detecting only changes in said radiation level whichoccur in said one frequency band for a predetermined number ofsequential sweeps through said frequency range of said transmittingmeans, and means for producing an electrical output signal only inresponse to said predetermined number of sequential detections in saidone frequency band.
 6. Apparatus as recited in claim 1 further includingmeans coupled between said detecting means and said indicating means forsensing the presence of a person in said radiation field and producingan electrical signal indicative thereof and wherein said indicatingmeans is responsive only to the combined electrical signals from saiddetecting means and said sensing means.
 7. Apparatus as recited in claim1 wherein said passive tuned tank circuit comprises in series aninductance element, first and second capacitive elements, and a fusiblelink disposed in said circuit and susceptible to destruction by theapplication of radiofrequency energy above a preselected level. 8.Apparatus as recited in claim 1 wherein said tuned circuit deactivationmeans comprises means for transmitting swept radio frequency radiationat selectable first and second levels into a preselected volume ofspace, means colocated with said transmitting means for detecting saidswept radiofrequency radiation and responsive to a selected change insaid radiation level To produce an electrical output signal indicativeof the presence of said tuned circuit, and means coupled to saiddetecting means and to transmitting means for selecting the higher ofsaid first and second transmitting means output radiation levels for apreselected period of time said higher level being sufficiently high toburnout said fusible link in said tuned circuit.
 9. Apparatus as recitedin claim 8 further including means for indicating complete destructionof said fusible link.
 10. A tuned passive tank circuit for use with aradiofrequency pilferage control system comprising in series aninductance element, first and second capacitive elements, and a fusiblelink disposed in said circuit and susceptible to destruction by theapplication of radiofrequency radiation above a preselected level. 11.Apparatus as recited in claim 10 wherein said fusible link is formed ofan electrically conductive material wherein an electrical overloadadequate to destroy said link is induced by a radiofrequency radiationlevel of one hundred milliwatts.
 12. Apparatus as recited in claim 10wherein: said radio frequency pilferage control system employs sweptradio frequency radiation, and said tuned passive tank circuit is tunedsuch as to absorb radiation over a frequency range less than and withinthe range of radiofrequencies over which said pilferage control systemis swept.